The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A research and development of a lean burn engine has been conducted to enhance energy efficiency and reduce carbon dioxide (CO2) emission.
However, the lean burn engine includes a large amount of oxygen in the exhaust gas such that it is difficult to remove nitrogen oxides (NOx) even though carbon monoxide (CO) and hydrocarbon (HC) included in the exhaust gas can be easily removed using an existing aftertreatment method.
In case of a diesel particulate filter coated with selective catalytic reduction (SDPF), a selective catalytic reduction (SCR) is coated to a porous diesel particulate filter (DPF) for causing reaction of NH3 supplied from a front end of the SDPF and nitrogen oxide (NOx) in the exhaust gas to thereby purifying NOx into water and N2.
Further, since the SDPF serves to function as a filter, the SDPF collects particulate materials (PMs) in the exhaust gas and increases a temperature of the exhaust gas through post-injection in the engine such that PMs collected in the SDPF can be oxidized/removed.
The SDPF can be classified into a passive type and an active type, and a passive type diesel particulate filter is coated with nitrogen oxide lean NOx trap (LNT)+selective reduction catalyst. When the nitrogen oxide collected in the nitrogen oxide LNT is dissolved through post-injection, NH3 is generated as a byproduct and NH3 and excessive nitrogen oxide in the exhaust gas are purified in the SDPF.